The present invention relates generally to a stereoscopic imaging optical system, and more particularly to an optical system for stereomicroscopes such as operating microscopes.
A stereomicroscope, because of being capable of having a three-dimensional grasp of a minute area, is used in a variety of fields such as studies, inspections, and operations.
A conventional stereomicroscope is of two types: one comprising two independent zoom optical systems for the left eye and the right eye, and another comprising one optical system common to both eyes.
The former is typically set forth in Patent Publication 1, and the latter is typically shown in Patent Publication 2.
There is also a microscope (electron image microscope) wherein an electronic imaging device is located at an imaging position for a viewing optical system, and a stereoscopic image is viewed through a stereoscopic display device instead of an eyepiece lens. An exemplary optical system for the electron image microscope is typically set forth in Patent Publication 3.
A video camera is well known as an electronic imaging apparatus having a zoom optical system. A typical one is shown in Patent Publication 4.
FIG. 17 is illustrative of the first example of the prior art stereomicroscope.
This stereomicroscope comprises a common objective lens for both eyes, a left-and-right pair of afocal zoom lens systems, a left-and-right pair of afocal relay optical systems and a left-and-right pair of imaging optical system.
FIG. 18 is illustrative of the second example of the prior art stereomicroscope.
This stereomicroscope comprises a common objective lens for both eyes, an afocal zoom optical system common to both eyes and coaxial with the objective lens, an afocal relay optical system common to both eyes and coaxial with the objective lens and a left-and-right pair of imaging optical systems.
Such a conventional stereomicroscope as depicted in FIG. 17 has a long total optical length on an image side with respect to the objective lens (a distance from the object-side surface of each afocal zoom optical system to the image plane of each imaging optical system) for the following two main reasons.    1. One reason lies in the optical arrangement per se.
This is chiefly because the following constraint conditions are satisfied.    1-1. Each unit has an independent role.
There are distinctive functions: the afocal zoom optical systems are capable of zooming, and the imaging optical systems are capable of imaging.    1-2 Between the individual units there is an afocal connection.
The afocal connection here means that light rays from an axial object point come substantially parallel out of the zoom optical systems, and enter the imaging optical systems.
This arrangement has one advantage of easy unit replacement.    2. Another reason lies in the optical layout involved (inherent in an optical microscope).
For an optical stereomicroscope it is required to bring a working space (on an operator side) close to a viewing position (an eyepiece lens) thereby allowing the operator to work easily. To this end the arrangement must be laid out such that an optical path from the objective lens to the eyepiece lens is bent. However, allowing for space for locating optical path-bending prisms or the like would render the optical path longer.
Such a conventional stereomicroscope as depicted in FIG. 18, too, has a long total optical length on an image side with respect to the objective lens (a distance from the object side surface of the afocal zoom optical system to the image plane of each imaging optical system) for the following two main reasons.    1. One reason lies in the optical arrangement per se.
The afocal relay optical system projects an image from an aperture stop onto near the object side of the afocal zoom optical system to keep low the height of off-axis rays near the objective lens and the afocal zoom optical system. This works in favor of diameter reductions near the objective lens and the afocal zoom optical system. Especially for the type comprising the common afocal zoom optical system for both eyes, the afocal relay optical system works in favor of diameter reductions.
However, the afocal relay optical system accounts for a large part of the total optical length. In other words, reducing the size of the afocal relay optical system is effective for reductions of the total optical length.    2. Another reason lies in the optical layout involved (inherent in the optical microscope).
Like such a conventional stereomicroscope as depicted in FIG. 17, there is a constraint condition for optical path bending.
In Patent Publication 3, there is an electron image microscope set forth, in which an entrance pupil position is located between an objective optical system and an object (subject) to keep good perspective. There is nothing disclosed about the possibility of size reductions incidental upon electronization.
In Patent Publication 4, there is an optical system for video cameras set forth, which is a 2D optical system for taking one image per one object, not that for stereoscopic imaging. There is nothing stated about a possible application to a stereomicroscope for stereoscopic viewing.
If a stereomicroscope is designed for electronic imaging, there is then none of the constraints of the aforesaid optical layout. The electron image microscope gives relative freedom to the relative position between working space (on the operator side) and the viewing position (stereoscopic display device). The electron image microscope with an electronic imaging device located at an imaging position is designed to convert an optical image into electric signals for displaying it on the stereoscopic display device. Between an imaging system and a display system there is an electric connection that enables the stereoscopic display device to be located at a free position. To have an optical system fit for the electron image microscope, it is important to reconsider the optical arrangement per se while taking the above merits (lifting off the constraint conditions) into account.
Patent Publication 1: JP(A) 2004-109487
Patent Publication 2: JP(A) 10-282428
Patent Publication 3: JP(A) 2006-158452
Patent Publication 4: JP(A) 2000-206407